1. Field of the Invention
This invention relates to a navigation apparatus mounted on a vehicle for indicating the current position thereof on a reduced-scale road map which is displayed on a screen together with a measuring scale corresponding to the reduced scale thereof.
2. Description of the Prior Art
Conventionally various navigation apparatii to be mounted on a vehicle for indicating the current position thereof on a road map bearing a reduced scale displayed on a screen have been disclosed, a case in point being one disclosed in Japanese Patent Laid-Open No. 62-164086, whose construction is shown in a block diagram in FIG. 6.
In FIG. 6, reference numeral 30 denotes an azimuth sensor adopting an earth magnetism sensor for detecting the absolute direction in which the vehicle is heading for, and reference numeral 31 denotes another azimuth sensor adopting an optical gyro sensor for detecting the relative azimuth. Numeral 32 denotes a speed pulse sensor for generating repetitive pulses in accordance with the speed of the vehicle, and numeral 33 denotes an operation switch for the driver to specify a road map to be displayed and so forth. An external storage means 34 stores various road maps, and the amplifier 36 amplifies an audio signal representing a crossroads, a building and so forth received from a microprocessor 29 and informs it to the driver by way of a speaker 37. Further, the microprocessor 29 receives signals from the azimuth sensors 30, 31, the speed pulse sensor 32 and from the operation switch 33, and controls the external storage 34 and the amplifier 36, and then generates a display signal, whereby the display unit 35 displays in accordance with the signal fed from the microprocessor 29.
Operation of the vehicle-mounted navigation apparatus constructed as above is now described. The pulse received from the speed pulse sensor 32 is accumulated in the microprocessor 29 so as to calculate the travel distance of the vehicle, and by the thus calculated travel distance data and running direction data generated from the azimuth sensors 30 and 31, the current position of the vehicle is detected. The microprocessor 29 thereafter reads road maps, various running conditions such as crossroads, buildings and so on, and also distance data representing a real travel distance per predetermined length on a selected road map from the external storage means 34, and then displays on the screen of the display unit 35.
By this operation above, a current vehicle position indicating mark 12 is indicated at a predetermined location on the road map displayed on the screen of the display unit 35 as shown in FIG. 7, and the real distance is calculated from the scale indication pattern 13d showing a real distance of a predetermined length on the road map displayed on the screen of the display unit, whereby the driver can conceive the real running distance heading for targets such as a crossroads, post office and so forth.
However, since the conventional vehicle-mounted navigation apparatus is constructed as above, the distance data represented by a measuring scale showing the reduced scale of a road map is displayed only at a predetermined location on the road map, so that it is not very effective for detecting a distance, for example, to the crossroads 14 from the current position of the vehicle, and therefore it is not easy for the driver to obtain the distance at only one glance.